Interplay Between Long-Range And Short-Range Interactions In Polymer Self-Assembly And Cell Adhesion
01 Jan 2008-
TL;DR: In this paper, reversible gelation of associating polymers and ligand-receptor interactions in membrane adhesion was studied, and the energy barrier of the adhesion as a result of membrane bending deformations and the double-well adhesion potential was calculated.
Abstract: Interplay between long-range and short-range interactions is a common theme in soft and biological matter, which results in complicated self-assembly behaviors. We study two examples of this interplay: reversible gelation of associating polymers and ligand-receptor interactions in membrane adhesion. In associating polymer solutions, the competition between the conformation flexibility of polymer chains and the enthalpic monomer interactions results in phase-separated micro-structures at the mesoscopic scale; both gelation and the microphase order-disorder transition are manifestations of this self-assembly. We further establish that reversible gelation is similar to the glass transition: both are characterized by ergodicity breaking, aperiodic micro-structures, and non-equilibrium relaxations over a finite temperature range. In the study of ligand-receptor interactions between surfaces, we emphasize the interplay between specific ligand-receptor binding, and generic physical interactions. We find that both the finite spatial extension of receptors and their mobilities affect their binding affinity. As a special case of the interplay between receptor binding and generic interactions, we study the dynamics of membrane adhesion that is mediated by receptor binding but fulfilled through membrane deformations. We calculate the energy barrier of the adhesion as a result of membrane bending deformations and the double-well adhesion potential, and analyze the different scenarios according to the shape of the adhesion potential by scaling arguments.
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01 Mar 1996
TL;DR: In this paper, a mean-field phase diagram for conformationally symmetric diblock melts using the standard Gaussian polymer model is presented, which traverses the weak- to strong-segregation regimes, is free of traditional approximations.
Abstract: A mean-field phase diagram for conformationally symmetric diblock melts using the standard Gaussian polymer model is presented. Our calculation, which traverses the weak- to strong-segregation regimes, is free of traditional approximations. Regions of stability are determined for disordered (DIS) melts and for ordered structures including lamellae (L), hexagonally packed cylinders (H), body-centered cubic spheres (QIm3m), close-packed spheres (CPS), and the bicontinuous cubic network with Ia3d symmetry (QIa3d). The CPS phase exists in narrow regions along the order−disorder transition for χN ≥ 17.67. Results suggest that the QIa3d phase is not stable above χN ∼ 60. Along the L/QIa3d phase boundaries, a hexagonally perforated lamellar (HPL) phase is found to be nearly stable. Our results for the bicontinuous Pn3m cubic (QPn3m) phase, known as the OBDD, indicate that it is an unstable structure in diblock melts. Earlier approximation schemes used to examine mean-field behavior are reviewed, and compa...
1,256 citations
554 citations
Posted Content•
TL;DR: It is shown that a system with competing interactions on different length scales, relevant to the formation of stripes in doped Mott insulators, undergoes a self-generated glass transition which is caused by the frustrated nature of the interactions and not related to the presence of quenched disorder.
Abstract: Using our previous results for the configurational entropy of a stripe glass as well as a variational result for the bare surface tension of entropic droplets we show that there is no disagreement between the numerical simulations of Grousson et al. and our theory. The claim that our theory disagrees with numerical simulations is based on the assumption that the surface tension is independent of the frustration parameter Q of the model. However, we show in this Reply that it varies strongly with Q and that the resulting Q-dependence of the kinetic fragility agrees with the one obtained by Grousson et al. We believe that this answers the questions raised in the Comment by Grousson et al.
127 citations
TL;DR: In this paper, eine Einfiihrung in einige aktuelle Forschungsaspekte aus dem Bereich der Biophysik zu geben is discussed.
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18 citations
Journal Article•
TL;DR: The selectivity of cell-cell and cell-tissue adhesion is determined by specific short range forces between cell surface proteins, which function as constraint reaction spaces facilitating the local assembly of actin stress fibers and control cell signalling processes.
Abstract: The selectivity of cell-cell and cell-tissue adhesion is determined by specific short range forces between cell surface proteins. Long range entropic interfacial forces (mediated by repeller molecules and membrane undulations) and adhesion-induced elastic stresses in the cell envelope serve the fine control of the strength and duration of adhesion. The initial step of cell adhesion exhibits typical features of a first order wetting transition resulting in the formation of tight adhesion domains by lateral phase separation of receptors. External lift forces can cause shrinking and unbinding of adhesion sites if the receptors are immobile but induce domain growth if they are mobile. Strong adhesion domains (resisting nano-Newton forces) can form by commitment of some 10,000 receptors enabling cells to control adhesion strength rapidly by varying the receptor and repeller densities on cell surfaces through endocytosis and exocytosis. The adhesion domains can function as constraint reaction spaces facilitating the local assembly of actin stress fibers and control cell signalling processes as shown for the activation of immunological responses by immunological synapses.
12 citations
References
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TL;DR: In this paper, a fluctuation theory of diblock copolymer melts was developed, which would include short-range fluctuations, and the correlation function S(q) was obtained within the Hartree approach by solving the integral equation.
Abstract: We attempt to develop a fluctuation theory of diblock copolymer melts, which would include short-range fluctuations. The one-loop correction has been found to have an ultraviolet divergence, which is shown to be architecture-dependent. The correlation function S(q) is obtained within the Hartree approach by solving the integral equation. However the solution cannot be related to experiments, because of the architecture-dependence of the divergence. We conclude that construction of the fluctuation theory with the use of the RPA-derived Hamiltonian is impossible.
27 citations
"Interplay Between Long-Range And Sh..." refers methods in this paper
...The random-phase approximation used in deriving the Hamiltonian, the approximation of higher-order interactions as spatially local, and the truncation at quartic order in the order-parameter expansion—all introduce inaccuracies whose effects are difficult to evaluate (Kudlay and Stepanow, 2003)....
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TL;DR: The adhesion between two approaching surfaces, one containing tethered ligands and the other receptors, is studied theoretically using the reaction-diffusion formalism and it is shown that the range of adhesion lr is generally determined by a combination of tether dynamics, ligand-receptor affinity and experimental speed of approach v.
Abstract: We study theoretically the adhesion between two approaching surfaces, one containing tethered ligands and the other receptors. Using the reaction-diffusion formalism, we show that the range of adhesion lr is generally determined by a combination of tether dynamics, ligand-receptor affinity and experimental speed of approach v. Contrary to previous studies, we fully account for back reactions and are thus able to describe the crossover between irreversible adhesion at large affinities or high speed v and reversible adhesion at small affinities or low speed. We also briefly discuss the case of rupture and show that in the limit of irreversible adhesion the rupture occurs always at a larger distance than lr determined for approaching surfaces.
26 citations
TL;DR: This paper first reviews the various techniques and related results about binding and unbinding, at the scale of a unique ligand/receptor couple, and shows how the physics of colloids associated with the growing scientific background concerning molecular recognition helps in rationalizing and inventing new diagnostic strategies.
Abstract: Biomolecules have the well-known ability to build reversible complexes. Indeed, antigens and antibodies or adhesion molecules are able to recognize one another with a strong affinity and a very high specificity. This paper first reviews the various techniques and related results about binding and unbinding, at the scale of a unique ligand/receptor couple. One important biotechnological application arising from these recognition phenomena concerns immuno-diagnosis, which is essentially based on the formation of these specific complexes. We show how the physics of colloids associated with the growing scientific background concerning molecular recognition helps in rationalizing and inventing new diagnostic strategies. Finally the concept of colloidal self-assembling systems as biosensors is presented as directly impacting the most important questions related to molecular recognition and their biotechnological implications.
26 citations
TL;DR: The present picture of the thermo-elastic control of membrane processes based on concepts of local thermal equilibrium is still rudimentary and has to be extended in the future to account for the intrinsic non-equilibrium situation associated with the constant restructuring of the cellular compartments on a timescale of minutes.
Abstract: Elastic forces and structural phase transitions control the architecture and function of bio-membranes from the molecular to the microscopic scale of organization. The multi-component lipid bilayer matrix behaves as a pseudo-ternary system. Together with elastically and electrostatically mediated specific lipid?protein interaction mechanisms, fluid?fluid phase separation can occur at physiological temperatures. This can drive the transient generation of micro-domains of distinct composition within multi-component lipid?protein alloys, enabling cells to optimize the efficiency of biochemical reactions by facilitating or inhibiting the access of enzymes by distinct substrates or regulatory proteins. Together with global shape changes governed by the principle of minimum bending energy and induced curvature by macromolecular adsorption, phase separation processes can also play a key role for the sorting of lipids and proteins between intracellular compartments during the vesicle mediated intracellular material transport. Cell adhesion is another example of mechanical force controlled membrane processes. By interplay of attractive lock and key forces, long range disjoining pressures mediated by repeller molecules or membrane undulations and elastic interfacial forces, adhesion induced domain formation can play a dual role for the immunological stimulation of lymphocytes and for the rapid control of the adhesion strength. The present picture of the thermo-elastic control of membrane processes based on concepts of local thermal equilibrium is still rudimentary and has to be extended in the future to account for the intrinsic non-equilibrium situation associated with the constant restructuring of the cellular compartments on a timescale of minutes.
26 citations
TL;DR: The adhesion energy between biotinylated vesicles and avidin beads is modeled by incorporating the extension of the adhesive ligands above the surface brush of the vesicle according to the blob model of bidisperse polymer mixtures of Komura and Safran assuming the polymer brush at the surface of theVesicle is compact.
Abstract: The adhesion and bending modulus of polybutadiene-poly(ethylene oxide) block copolymer vesicles made from a bidisperse mixture of polymers is measured using micropipette aspiration. The adhesion energy between biotinylated vesicles and avidin beads is modeled by incorporating the extension of the adhesive ligands above the surface brush of the vesicle according to the blob model of bidisperse polymer mixtures of Komura and Safran assuming the polymer brush at the surface of the vesicle is compact. The same model accurately reproduces the scaling of the bending modulus with polymer composition.
25 citations
"Interplay Between Long-Range And Sh..." refers background in this paper
...On the other hand, artificially-designed bio-mimetic materials, such as polymersomes (Discher et al., 1999; Lin et al., 2004; Bermúdez et al., 2004; Lin et al., 2005), vesicles or liposomes (Cuvelier et al....
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